Amlodipine: Increased systemic exposure of simvastatin. Increase in systemic exposure w/ diltiazem (CYP3A4 inhibitor). Increased plasma conc w/ strong CYP3A4 inhibitors eg, ketoconazole, itraconazole, ritonavir. Exposure may be increased w/ grapefruit juice. Valsartan: Increased incidence of hypotension, hyperkalemia & changes in renal function w/ dual blockade of RAS w/ ARBs, ACE inhibitors, or aliskiren. Increased K levels w/ K supplements, K-sparing diuretics, salt substitutes containing K, or other drugs that may increase K levels (heparin). Attenuation of antihypertensive effect & increased risk of worsening of renal function w/ NSAIDs including selective COX-2 inhibitors. Increased serum lithium conc & toxicity. Increased systemic exposure w/ inhibitors of OATP1B1 (rifampin, ciclosporin) or MRP2 (ritonavir).